In recent years, an MPLS network that performs packet transfer using a label switching technique has been widely utilized. The MPLS network sets a Work path and a Protection path as different paths. Therefore, even when the Work path has a fault, the MPLS network can communicate by using the Protection path.
However, to realize a network having high reliability by using the technique, it is important to switch from the Work path to the Protection path at high speed and to shorten the time that the communication status is disconnected as much as possible when a fault occurs. A technology for speeding up the switching between paths has been known as disclosed in, for example, Japanese Laid-open Patent Publication No. 2002-374288. In the technology disclosed in Japanese Laid-open Patent Publication No. 2002-374288, when the fault of a current path (Work path) is detected, high-speed switching to a preliminary path (Protection path) is realized by writing that the current path is shut down into a routing table.
However, a conventional path switching technology, including the above technology, cannot sufficiently cope with a link aggregation (hereinafter, LAG) function that bundles up a plurality of physical lines and treats the lines as one virtual line. A virtual line made by using LAG can continue communication without problems except that a bandwidth decreases even when a part of a physical line has a fault.
For this reason, if we want to avoid a communication disconnection even for a fraction of time when using a virtual line made by using LAG, it is preferable to maintain the status without the switching between paths when a part of a physical line has a fault. On the other hand, if we want to avoid the reduction of a bandwidth, it is preferable to perform the switching between paths when a part of a physical line has a fault.
In this way, when using a virtual line made by using LAG, whether the switching between paths should be performed depends on the purposes for which the line is being used when a part of a physical line has a fault. There is a problem in that the conventional path switching technology cannot cope with the requirement for using a virtual line made by using LAG.